Hitherto, there has been studied a technique for mounting an IC package such as a CPU or an LSI on a printed circuit board through the intervention of a socket. In most motherboards of a variety of semiconductor devices, e.g., a personal computer and a server, a socket is mounted therein for attachment of a CPU implemented in an LGA or BOA package thereto.
The CPU has been made to have more pins and a faster operation speed every year in order to improve its function and performance. To cope with such requirements, the CPU package has been made to have a larger size while having a finer pin pitch.
Accompanied with this, the socket is required to cope with the ever-increasing number of pins while coping with problems such as an increase in the amount of bending thereof in response to the increase in the package size or a difference in height of contact lands or balls of the package. Hence, it is desired to provide a structure capable of securing a sufficient stroke of a socket contact.
Moreover, as a countermeasure to the fine pitch requirements, it is important to decrease the size of the socket contact, and it is desirable to be able to provide secure contact between IC pins and socket contacts under suitable contact pressure.
Furthermore, as a countermeasure to the fast operation speed requirements, it is important for a contact terminal to have a low inductance, and it is desired for the contact terminal to have a low contact resistance and a high allowable current to cope with an increase in the consumption current in response to the faster operation speed.
Current LGA package sockets mainly have 400 to 800 pins having a pitch of about 1 mm and are fabricated using a method of complicatedly folding a metal plate to form contact terminals having a predetermined shape and inserting the contact terminals in a socket housing. Such a conventional technique is disclosed in Patent Documents 1 and 2, for example.
Patent Document 1: Japanese Patent Application Laid-Open No. 2004-158430
Patent Document 2: Japanese Patent Application Laid-Open No. 2005-019284
Patent Document 3: U.S. Pat. No. 6,669,490
However, in the conventional technique disclosed in Patent Documents 1 and 2, the contact terminal is of a plate spring type, and thus, when the spring length is increased to increase the stroke of the contact terminal, the contact terminal may make contact with adjacent pins. Therefore, there is a problem that it is difficult to increase the stroke when the pins are made to have a finer pitch.
Moreover, in order to resolve such a problem, Patent Document 3 has proposed a technique that uses a structure using a column formed of a conductive elastomeric member in the contact terminal. In this case, since the repulsive properties of a socket are determined by the characteristics or the structure of the conductive elastomeric member, as long as it is possible to find a conductive elastomeric member exhibiting a suitable repulsive force, it is possible to realize a socket capable of securing a sufficient stroke under a desired load.
However, when the conductive elastomeric member as disclosed in Patent Document 3 is used, since the contact terminal is not a metal but an elastomeric member, the contact resistance is high compared with a metallic contact and there is a fear of an increasing possibility of heat generation or voltage drop in response to higher current consumption. Moreover, since the contact terminal does not wipe a metallic land when it is inserted to be fitted in a package, there occurs a new problem that it is difficult to remove an oxide film formed on a land.